First off, have you power cycled your router since this has happened? If not, just unplug it for about 20 seconds then just plug it back it. Routers need to be rebooted sometimes too. I used to have a D-link that I would have to reboot a couple times a week because it would either crash or loose connection intermittently. An occasional reboot would fix this. I switched to Linksys (made by Cisco) because they are probably the best home use routers on the market. If it still does it, read on.
If you are wireless, I am sure your key is correct since the Wii wont finish setup if it is not. Also, have you tried assigning your wii a static address?
Depending on your network you need to know what your address scheme is. I dont know how much you know about home networking so I will try and walk you through it as best as I can.
First, go to your home PC and go to Start/Run, then type in CMD and hit enter.
A black window will open. Next type "ipconfig" (leave the quotes out) and hit enter. This should tell you what your IP address is. Usually it will be either:
192.168.0.xxx or 192.168.1.xxx if your router was setup with the default address. So all you are concerned about is the first 3 number sets (192.168.?) so we know what the network is. Usually a router is setup to normally use about 50 address for DHCP (addresses the router will hand out when a computer is set to obtain address automatically) and the rest can be used as static addresses (ones that will never change).
So once you determine your ip address scheme, to make things easier just use something like:
192.168.x.201 ("x" being 0 or 1 normally) in your wii. Now I can't remember if the Wii asks for this stuff or not since I am not near mine now is the Subnet mask and the Default Gateway. So your setup should look like this.
IP Address: 192.168.x.201
Subnet Mask: 255.255.255.0
Default Gateway:192.168.x.1 (the local address of your router)
and also I can't remember if it asks for a DNS address or not. That too will also be your router address (192.168.x.1)
DHCP can act up sometimes but very rarely. Try this and see what happens.
If you have problems, you can look me up in AIM under R8DERHED5150